1. Field of the Invention
The present invention relates to an antifuse for a memory device. More particularly, it relates to an apparatus for stabilizing an antifuse used for a memory device.
2. Description of the Prior Art
In general, an antifuse is the opposite element of a fuse. In a programming process, the antifuse is electrically connected, whereas the fuse is electrically blown.
A basic configuration of the antifuse is similar to a capacitor. If the antifuse is programmed, an insulating material in the middle of the antifuse is broken so that the antifuse is electrically connected.
Using the antifuse has various advantages in a semiconductor fabrication. That is, an area used for a fuse can be reduced, a repair is possible after a package process, and the size of the antifuse can be linearly reduced with another parts in opposition to the fuse.
However, a major problem among many other problems occurring when using the antifuse is the instability of the antifuse.
The antifuse has the following problems:
First problem is that the antifuse is not programmed although the program process has already performed (i.e, an electrical connection is not achieved).
Second problem is that a program is deleted in the reading process after the antifuse is programmed (i.e., an electrical connection is cut again).
A third problem is that in an antifuse not programmed is programmed in the reading process (i.e., unexpected programming occurs by a low voltage).
In order to obviate the above problems, the prior art uses the following solutions:
As the first solution, in order to solve the first problem, a high voltage should be employed to stabilize the program the antifuse, and an antifuse whose insulation is easily broken should be also employed.
However, making the high voltage is a burden on a circuit and exerts a bad influence on peripheral circuits. Also, the antifuse which often has an insulation breakdown creates the aforementioned third problem.
As another solution, a voltage when programming is separated from a voltage when reading, so that a read voltage becomes lowered to prevent an unexpected programming, thereby achieving a stabilization of the antifuse.
Hereinafter, technical terms to be used in this specification are defined as follows:
`An appropriate applying voltage` of the antifuse is a voltage between both ends of one antifuse, and means a read voltage which does not induce unexpected programming or unexpected deletion (for example, a programmed antifuse returns to cut state).
Let us suppose that a high voltage which has to programm the antifuse when a program has been intended is "a program voltage" of the antifuse.
The "appropriate applying voltage" and the "program voltage" are changed in response to a structure and shape of the antifuse.
If the "appropriate applying voltage" of the antifuse becomes a power-supply voltage of the peripheral circuits, "the program voltage" requires a very high voltage. In most of cases, the "program voltage" is three times or seven times larger than the "appropriate applying voltage".
On the contrary, if the "program voltage" of the antifuse becomes a power-supply voltage (Vcc or Vpp) of the peripheral circuits, a lower voltage than the power-supply voltage Vcc of the peripheral circuits is required as the "appropriate applying voltage". Assuming that the antifuse is programmable by a power-supply voltage Vcc, the "appropriate applying voltage" should be below 1/2 Vcc.
In this manner, if a voltage different from the power-supply voltage of the peripheral circuit is employed, a level shifting is required for transmitting a signal to the peripheral circuit, thereby requiring a supplementary circuit.